Super pressure electrode-insulator



March 21, 1961 G. T. ANGELOFF SUPER PRESSURE ELECTRODE-INSULATOR Filed Jan. 20, 1958 FURNACE FlG- 2 FIG-l INVENTOR.

GEORGE T. ANGELOFF Y United States Patent SUPER PRESSURE ELECTRODE-INSULATOR George T. Angeloif, North Branford, Conn., assignor to Olin Mathieson Chemical Corporation, a corporation of Virginia Filed Jan; 10,195; Ser. No. 709,954 a s cute-13s The present invention relates to electrodes and in particular to the manufacture of electrode-insulator assemblies capable of withstanding super pressures; i.e., pressures of the order of 50,000 lbs. per square inch.

A particular feature of the inventionis the provision of a novel method of manufacturing such an electrodeinsulator assembly.

' Another feature of the invention is the provision of a process for the manufacture of an electrode-insulator assembly which includes the step of firing the insulator and hardening the metal housing surrounding the in-- sulat'or in one operation.

T A still further feature of the invention is the provision of a process useful in the manufacture of electrode-insulator assemblies which is effective, when the insulator i's di-sposedwithin a housing, to seat the entire exterior surface or face of the insulator against a corresponding surfaceof the housing without the need for grinding and lapping.

Another feature ofthe invention is the provision of a process in the manufacture of electrode-insulators which is'inexpensive to practice.

A process embracing the principles of the present invention may comprise, the steps of providing a heat hardenable metallic housing having a tapered bore, providing an unfired ceramic insulator, machining a taper on the outer surface of the insulator corresponding to the taper of said tapered bore, inserting the unfired insulator into the metallic housing so that the tapers mate, and heating the assembled insulator and housing to fire the insulator and to harden the housing.

Other features and advantages of the present invention will become more apparent from a study of the succeeding specification when read in conjunction with the appended drawings, in which:

Fig. l is a mid-sectional view of an electrode-insulator assembly manufactured in accordance with the process of the present invention;

Fig. 2 is a mid-sectional view of an insulator and its housing illustrating the disposition of the elements at the time of firing;

Fig. 3 is a mid-sectional view of the insulator, and;

Fig. 4 is a side view of the electrode.

Referring now to Fig. 1 there is shown a typical super pressure electrode-insulator assembly including a housing 10, an insulator 11, and an electrode 12, an insulating w'asher 13, a lock nut 14, and a terminal nut 16.

It is to be understood that although the material from which the insulator in the exemplary embodiment of the invention is made is known as Lava-Grade A, supplied by the American Lava Corporation, Chattanooga, Tennessee, a variety of other ceramics may be substituted.

Examples of such other ceramics are steatite, cordieriete, mullite and the like.

correspondingly, although the present embodiment of the invention calls for a steel housing fabricated from 440 C stainless, it is entirely within the scope of the invention to substitute any heat hardenable steel.

: moval from the furnace. 7

Upon removal from the furnace, an examination of eluded angle is' about 10. t

' ert atmosphere.

In the practice of the present invention the steel housing 10 is provided with a tapered bore -17 where the included angle substended by the taper falls within the minimum value of and the maximum value of 90. In the illustrated embodiment ofthe invention the in- A length of unfired Grade A Lava is machined to the general configuration shownin Fig. 3. A taper having a included angle is formed on the exterior surface and the interior-is bored andcounterbored to provide a sliding fit for the electrode '12 of Fig. 4. g

Next the unfired insulator-is placed within the hous-- ing 10 as shown in Fig. 2 andthereafter the assembly is disposed within a cool furnace so that the larger diameter of the insulator .is facing upwardly. Preferably, but not necessarily, a light weight W, in this instance a 20 gram weight, is disposed as shown in Fig. 2 to urge the insulator into contact with the housing.

An atmosphere of nitrogen is then introduced to the furnace. As is well known in the art nitrogen is utilized to prevent oxidation and to provide a generally in- Thereafterv the furnace temperature is raised to about 1950 F. at a ratenot-exceeding 500 per hour. The l950 temperature is held for about minutes. Next the source of heat is cut off and the assembly is oven cooled to about 250 F. before re-t the stainless steel housing reveals a hardness of 42 to 44 Rockwell C Scale while the electrical resistance of the assembly measured from the electrode 12 to the hous ing 10 is of the order of 15 megohms.

A static pressure of about 50,000 pounds per square inch applied to the insulator-electrode assembly, as shown in Fig. 1, and in a direction which tends to urge the insulator towards the small diameter of the taper is effective to move the insulator into snug contact with its housing (usually approximately 0.010 inch measured along the longitudinal axis of the assembly) does not fail the insulator.

correspondingly, when the unit is placed in threaded engagement with a high pressure vessel and used in the fashion of a spark plug to ignite a monopropellant charge, the ceramic insulator stands up well. Dynamic pressures in excess of 50,000 pounds per square inch have no harmful effect upon the electrode-insulator assembly.

It is to be understood that the process of the present invention may be utilized to insulate or to develop electrode-insulator assemblies useful in other fields such as, for example, the provision of a super pressure plug for housing a thermocouple where the thermocouple is insulated from its housing in the same fashion that the electrode 12 is so insulated.

It is especially important to note that the practice of the present process steps provide an inexpensive way to provide an insulated electrode which is operable in super pressure ranges. Heretofore, it has been necessary to laboriously grind and lap fired ceramic insulators with respect to a metallic housing so as to provide uniform surface contact between the insulator and its housing to avoid stress concentrations which crack the insulator.

It is anticipated that a variety of electrode-insulator assemblies may be devised with the practice of the process steps of the present invention without departing from the spirit and scope thereof.

What is claimed is:

1. A process for manufacturing a super pressure insulated electrode capable of withstanding shock pressures of the order of 50,000 p.s.i. generated over intervals as short as millisecond comprising the steps of providing a heat hardenable metallic housing having a tapered bore, said housing being fabricated of type Patented Mar. 21, 1961 440 stainless steel, providing an unfired ceramic insulator, machining a taper on the outer surface of the in: sulator corresponding to the tapered bore of the housing, inserting,the unfired insulatorinto the metallic housing. so that the taper and the tapered bore mate, and heating the assembled insulator and housing to a temperature of about 1950 F. at a rate not exceeding 500 per hour to fire the, insulator and to harden the housing and furnace cooling the insulated electrode to about.

2. A process for manufacturing a super pressure insulated electrode capable. of withstanding shock pressures of the order of 50,000 p.s.i. generated over inrtervals as short, as l millisecond comprising the steps of providing aheat hardenable metallic housing having a tapered bore, saidthousing' being fabricated of type 440 stainless steel, providing an unfired ceramic insulator, machining a taper on the outertsurface of the insulator corresponding to. the tapered bore of, the housing, inserting the unfired insulator into, the metallic housing so that the taper and the tapered bore mate, applying pressure upon the ceramic insulator which tends to move the insulator relative to the housing and heating the assembled insulator and housing to a temperature of about-1950 F. at a rate not exceedingv 500 per hour to fire the insulator and to harden the housing and furnace cooling theinsulated electrode to about 250 F.

3. A process for manufacturing asuper pressure insulated electrode capable of withstanding shock pressures of the order of 50,000 p.s.i. generated over intervals as,

short as millisecond comprising, the steps of providing a heat hardenable metallic housing having a tapered bore, said housing 'beingfabricated of type 440 stainless steel,,providing an unfired ceramic insulatonmachining a taper on the outer surface of the insulator correspond, ing, to the tapered bore of, the housing, inserting the un fired insulator into the metallic housing so that the taper and the tapered bore mate, applying pressure upon the ceramic insulator which tends to movethe insulator relative to the housing and applying heat to the assembled insulator and housing, to a temperature of about 1950 F. at a rate of about 500 per hour to fire the insulator and to harden the housing and furnace cooling the insulated electrode to about 250 F.

4. A process for manufacturing a super pressure in 4 sulated electrode capable of withstanding shock pressures of the order of 50,000 p.s.i. generated over intervals as short as millisecond comprising the steps of providing a heat hardenable stainless steel housing having a tapered bore, said housing being fabricated of type 440 stainless steel, providing an unfired ceramic insulator, machining a taper on the outer surface of the insulator corresponding to the tapered bore of the housing, inserting the unfired insulator into the metallic housing so that the taper and the tapered bore mate, disposing the assembled insulator and housing so that the'taper flares upwardly and outwardly, applying pressure upon the ceramic insulator whichtends to move the insulator relative to the housing and heating the assembled. insulator and housing to a temperature of about 1950 F. at a rate not exceeding 500 per hour in a nitrogen atmosphere to fire the insulator and to harden the housing and furnace cooling the insulated electrode-to about 250 F.

5. A process for, manufacturing a super pressure insulated electrode capable of withstanding shock pressures of the order of 50,000 p.s.i. generated over intervals as short as millisecond comprising the steps of providing a heat hardenable metallic housing having a tapered here, said housing being fabricated of type 440 stainless steel, providing an unfired ceramic insulator, machining a taper on the outer surface of the insulator corresponding to the tapered bore of the housing, inserting the unfired insulator into the metallic housing so that theta per and the tapered bore mate, and heating the assembled insulator and housing to a temperature of about 1950 F. at a rate not exceeding 500 per hour in an atmosphere of nitrogen to fire the insulator and to harden.

the housing and furnace cooling the insulated electrode to about 250 F.

References Cited in the file of this patent UNITED STATES PATENTS.

974,008 Wolff Oct. 25, 1910 2,469,211 Schwartzwalder et al. May 3, 1949 2,699,158 Purdy et al. Jan. 11, 1955 2,784,112 Nicholson Mar. 5, 1957 OTHER REFERENCES 7 Republic Enduro Stainless Steels, Republic Steel Corp, pages 48-52, 1951. t 

1. A PROCESS FOR MANUFACTURING A SUPER PRESSURE INSULATED ELECTRODE CAPABLE OF WITHSTANDING SHOCK PRESSURES OF THE ORDER OF 50.000 P.S.I GENERATED OVER INTERVALS AS SHORT AS 1/2 MILLISECOND COMPRISING THE STEPS OF PROVIDING A HEAT HARDENABLE METALLIC HOUSING HAVING A TAPERED BORE, SAID HOUSING BEING FABRICATED OF TYPE 440 STAINLESS STEEL, PROVIDING AN UNFIRED CERAMIC INSULATOR, MACHINING A TAPER ON THE OUTER SURFACE OF THE INSULATOR CORRESPONDIG TO THE TAPERED BORE OF THE HOUSING, INSERTING THE UNFIRED INSULATOR INTO THE METALLIC HOUSING SO THAT THE TAPER AND THE TAPERED BORE MATE, AND HEATING THE ASSEMBLED INSULATOR AND HOUSING OT A TEMPERATURE OF ABOUT 1950*F. AT A RATE NOT EXCEEDING 500* PER HOUR TO FIRE THE INSULATOR AND TO HARDEN THE HOUSING AND FURNACE COOLING THE INSULATED ELECTRODE TO ABOUT 250*F. 